Examples of containers, devices, and members for high-pressure gas facilities, air-conditioning facilities, cold and hot-water supply equipment, and the like include a variety of valves including a high-pressure valve, a variety of joints, hydraulic containers such as a variety of valves, joints and cylinders, nozzles, sprinklers, water faucet clasps, and the like, and a copper alloy used for the above is joined with a copper pipe, a variety of members, and the like. Since a high pressure is applied to the joint portion, brazing is employed as a joining method from the viewpoint of reliability. Brazing produces a high joint strength and a high reliability, but the melting point of a brazing is high, approximately 700° C. to 830° C., and therefore a copper alloy to be brazed is also, accordingly, heated to a temperature of the melting point of the brazing or higher. However, since a copper alloy used for the above members generally has a melting point of approximately 850° C. to 950° C., there is a problem in that the material strength of a brazed copper alloy significantly decreases, and corrosion resistance degrades.
The above copper alloy is a cut hot-forged material, a cut extruded rod material, or a cut material of a cast metal and a continuously cast rod. Examples of the hot-forged material or the extruded rod material include a forging brass rod C3771 that is mainly based on JIS H 3250 standards and is excellent in terms of hot forgeability (typical composition: 59Cu-2Pb-remainder: Zn), a free-cutting brass C3604 that is excellent in cutting work (typical composition: 59Cu-3Pb-remainder: Zn), a copper alloy material obtained by substituting Pb in the above materials with Bi due to a recent demand for removing Pb, and dezincification corrosion resistant forging brass or dezincification corrosion resistant free-cutting brass in which the concentration of copper is increased to 61 mass % to 63 mass % in order to obtain excellent dezincification resistance.
Meanwhile, examples of the cast metal include CAC406 (85Cu-5Sn-5Zn-5Pb) which is a cast metal based on the standards of JIS H 5120 or JIS H 5121 or a continuously forged cast and a Cu—Sn—Zn—Pb alloy that is excellent in terms of corrosion resistance, a Cu—Sn—Zn—Bi alloy obtained by substituting Pb in the above alloy with Bi, brass cast metal CAC202 (67Cu-1Pb-remainder: Zn) that is excellent in terms of mold castability, CAC203 (60Cu-1Pb-remainder: Zn), and the like. However, when the above copper alloy is brazed, since the copper alloy is heated to a high temperature of approximately 800° C. or approximately 750° C., or at least 700° C. or higher, there is a problem in that the material strength decreases. Particularly, in a Cu—Zn alloy containing Pb, Bi, Sn, and the like, when the Cu concentration exceeds 64 mass %, the crystal grains coarsen such that the strength significantly decreases. In addition, the CAC406 alloy has a high Cu concentration, has had a problem of a low strength, and, furthermore, has a problem in that the strength decreases further. Meanwhile, when an alloy having 63 mass % or less of Cu, particularly, a Cu—Zn—Pb or Cu—Zn—Bi alloy is heated to a temperature of 700° C. or higher, particularly 800° C. or higher, the fraction of a β phase increases, and a problem occurs with the corrosion resistance. Furthermore, in a case in which the Cu concentration is low, since the fraction of the β phase increases, ductility or impact characteristics decrease.
General examples of a brazing material used for joining of a copper alloy such as a valve and a copper pipe or the like include a phosphor bronze brazing filler of JIS Z 3264 and a silver solder of JIS Z 3261. Among the above, a phosphor bronze brazing filler of BCuP-2 (typical composition: 7% P-93% Cu) is most frequently used, and a phosphor bronze brazing filler of BCuP-3 (typical composition: 6.5% P-5% Ag-88.5% Cu) and a silver solder of Bag-6 (typical composition: 50% Ag-34% Cu-16% Zn) are also frequently used. The melting points (solidus temperature-liquidus temperature) of the brazing filler metals are 710° C. to 795° C., 645° C. to 815° C., and 690° C. to 775° C. respectively, and the brazing temperatures are reported to be 735° C. to 845° C., 720° C. to 815° C., and 775° C. to 870° C. respectively in JIS standards. Therefore, while also depending on the kind of the brazing filler metal and the shape, thickness, and size of the copper alloy, the copper alloy such as a valve is heated to at least 700° C. or higher, approximately 800° C. over several seconds to several minutes, and non-directly heated portions also reach a high-temperature state. When the copper alloy is heated to at least 700° C. or higher, approximately 800° C., the above problem regarding pressure resistance or corrosion resistance occurs. Further, as a brazing method, there is a method in which a brazing filler metal is placed in a joint portion, and made to pass through a furnace heated to approximately 800° C., thereby performing continuous brazing. In this case, the entire copper alloy such as a valve is heated to 800° C., and cooled.
In addition, although not relating to characteristics after brazing, as a technique that decreases the β phase which degrades corrosion resistance, a technique in which a Bi-added free-cutting copper alloy composed of 60.0 mass % to 62.5% Cu, 0.4 mass % to 2.0 mass % Bi and 0.01 mass % to 0.05 mass % P with a remainder of Zn is hot-extruded, then slowly cooled so that the surface temperature of the extruded material becomes 180° C. or lower, then a thermal treatment is carried out at, for example, 350° C. to 550° C. for 1 hour to 8 hours so as to decrease the β phase and form a metallic structure in which the vicinity of the β phase is surrounded by an α phase, thereby securing favorable corrosion resistance is known (for example, refer to Japanese Unexamined Patent Application Publication No. 2008-214760). When the copper alloy is worked at a high temperature, since the amount of the β phase increases, corrosion resistance is secured by adding a slow cooling process after hot working as described above, and, furthermore, a thermal treatment process after cooling. However, in brazing, such slow cooling or a thermal treatment after cooling definitely leads to an increase in costs, and there is a problem in that the thermal treatment is difficult practically.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2008-214760.